Field of the Invention
The present invention relates to a method of estimating the temperature of magnets (hereinafter referred to as a “magnet temperature”) on a rotating member of a rotary electric machine.
Description of the Related Art
Rotary electric machines include a rotor and a stator that include magnets. When the temperatures of the rotor and the stator exceed a threshold temperature, the magnets start to become demagnetized. Therefore, it is necessary to appropriately manage the temperatures of the rotor and the stator in order to prevent the rotor and the stator from exceeding the threshold temperature. In order to carry out such temperature management, it is desirable to directly detect the temperatures of the rotor and the stator.
The temperature of the stator can easily be detected since the stator is fixed to the machine casing. However, since the rotor is a rotating member, it is more complicated to detect the temperature of the rotor. More specifically, the temperature of the rotor needs to be detected by reading a detection signal from a temperature sensor, which is mounted on the rotor through a slip ring, or on a rotary connector that is mounted on the shaft of the rotor. The mechanism for detecting the temperature of the rotor makes the rotary electric machine complex in structure and costly to manufacture.
Japanese Patent No. 4572907 discloses that the rotational speed of the rotor of a motor, the temperature of the stator coils of the motor, and the temperature of a coolant for cooling the stator of the motor are detected, and the temperatures of the magnets (magnet temperatures) on the rotor and the stator are estimated based on operating points (a torque command value and the rotational speed of the rotor) of the motor, the detected temperatures, and a thermal model between the magnets on the rotor and the stator.
Further, in Japanese Laid-Open Patent Publication No. 2000-023421, a stator-side oil-cooling system and a rotor-side oil-cooling system are provided separately, and cooling oil is circulated in each of the stator-side cooling system and the rotor-side cooling system. In the case of cooling the stator and the rotor, the temperature of the rotor is estimated based on an inflow temperature of the cooling oil prior to cooling the rotor, an outflow temperature of the cooling oil after cooling the rotor, the motor torque, and the rotational speed of the motor.